Often, discovering footprints in the sand will cause us to think of the people who may have left those footprints; however, for ancient peoples, their footprints have long disappeared and we are left with remnants of their existence. The economic history of an ancient Mayan city on the Yucatan Peninsula of Mexico has remained a mystery for over 1,500 years. We're talking to BYU environmental scientist Richard E. Terry about going beneath the surface of the ground to find the ruins of an ancient Mayan marketplace.—Original airdate: 3/19/2008